The present invention relates to a valve control apparatus for an internal combustion engine, which is able to vary a lift-amount characteristic or the like of an intake valve and/or an exhaust valve in accordance with an operating state of engine.
Japanese Patent Application Publication No. 2009-103040 discloses a previously-proposed valve control apparatus in the field. This valve control apparatus includes a holder which swings by being driven by a control cam, a sub-cam which is driven by an intake cam, first and second rocker arms which open and close first and second intake valves by being driven by the sub-cam, and a connection changeover mechanism which connects the first rocker arm with the second rocker arm or disconnects the first rocker arm from the second rocker arm.
The sub-cam includes a drive cam surface and a rest cam surface given for a minute lift. A lift-amount characteristic of each of the first and second intake valves can be continuously varied according to a swing position of the holder.
In a high-load region of engine, the connection changeover mechanism connects the first rocker arm with the second rocker arm so that the first and second intake valves are driven (opened and closed) by the drive cam surface of sub-cam. Thereby, an intake-air charging efficiency is enhanced to increase an output torque of engine.
On the other hand, in a low-load region of engine, the connection changeover mechanism disconnects the first rocker arm from the second rocker arm. Thereby, the first intake valve is driven by the drive cam surface of sub-cam, and the second intake valve is made substantially in a closed state (minute-lift state) by the rest cam surface. Because of this lift difference between the first and second intake valves, an intake-air swirl effect is produced in a cylinder, so that a combustion of the engine is improved. Hence, a fuel economy is improved.